Databases

• MusicTheory.net has everything from quarter notes to the Phrygian dominant scale; it’s a great place to learn to read and understand music.
• IMSLP (International Music Score Library Project) has free scores of just about anything in the public domain.
• The VMII Song Database is a catalogue with descriptions and translations of just about every classical song you could possibly want to know about.

Apps

I personally use every one of these apps. Some are free, some have an up-front cost, and some require a subscription, but I have researched and tested each of them and am confident that they are all the “best bang for your buck.”

Accompaniment:

Karaoke:

Metronome:

Rhythm Practice:

Pitch Practice:

Phonetics Education:

Music Theory Education:

Scanning Music: